1. Field of the Invention
The present invention relates to a speech signal processing apparatus, and more particularly, to a speech signal cutting-out apparatus for cutting out a speech signal from a noisy speech signal, a speech recognition apparatus for recognizing speech from an extracted speech signal, and a signal processing apparatus disposed ahead of a speech recognition apparatus.
2. Description of the Prior Art
In a conventional speech recognition apparatus, a speech signal is filtered from a noisy speech signal by a filter, and then, speech is recognized by a pattern matching method (See, for example, Japanese Laid-open Patent Publication (JP-A) No. 59-121099/1984 and the Japanese Laid-open Patent Publication (JP-A) No. 62-179000/1987). However, in the conventional speech recognition apparatus of this type, since a speech signal is filtered by the filter and noise included in the speech signal can not be completely removed from a noisy speech signal, a recognition rate for recognizing a speech is relatively low. In particular, when a speech signal including a large noise component is recognized by the conventional speech recognition apparatus, there is a problem in that the recognition rate is extremely low.
FIG. 22 shows a conventional speech signal processing apparatus.
Referring to FIG. 22, the conventional speech recognition apparatus comprises a speech detection section 451 for detecting a speech signal interval from an inputted noisy speech signal, a noise interval judgment section 452 for detecting a noise interval based on the speech signal interval detected by the speech detection section 451, a muting controller 453 for generating a control signal for muting a noisy speech signal for the detected noise interval in response to the noise interval detected by the noise interval judgment section 452 and a muting section 454 for muting the inputted noisy speech signal for the detected noise interval according to the muting control signal outputted from the muting controller 453.
In the conventional speech signal processing apparatus shown in FIG. 22, a speech signal interval is detected by the speech detection section 451, and the noise interval judgment section 452 detects a noise interval by inverting the speech signal interval detected by the speech detection section 451. Furthermore, the muting controller 453 generates the muting control signal for a noise interval detected by the noise interval judgment section 452, and then, an inputted noisy speech signal is attenuated only for the detected noise interval by the muting section 454.
However, in the conventional speech signal processing apparatus of this type, noise is not sufficiently suppressed from a noisy speech signal, and also a recognition rate for recognizing a speech is extremely low.